In the first part of my talk I will address the question whether the
morphology-density relation is instrinsic, or the result of more fundamental,
underlying relations between galaxy mass, environment and star formation activity.
In the second part I will describe our study of the evolution of the early-type
galaxy fraction with redshift based on stellar mass-selected samples of field
and cluster galaxies. Selecting galaxies by mass turns out to drastically
change the picture with respect to results based on luminosity-selected samples,
which are traditionally used for such analyses.